There have conventionally been known electrophotographic image forming apparatuses such as copying machines, printers, and facsimiles. An electrophotographic image forming apparatus forms an electrostatic latent image on a surface of a photoreceptor drum (toner image bearing member), develops the electrostatic latent image by supplying the photoreceptor drum with toner through a developing device, transfer, onto a sheet such as a sheet of paper, a toner image formed on the photoreceptor as a result of the development, and fixes the toner image onto the sheet through a fixing device.
In recent years, a two-component developer excellent in charging stability of toner has been commonly used in full-color and/or high-definition image forming apparatuses.
The two-component developer is composed of toner and carrier. The toner and the carrier are agitated in a developing device, whereby friction between the toner and the carrier is caused, and the friction allows the toner to be appropriately charged.
In the developing device, the charged toner is supplied, for example, onto a surface of a developing roller, and moved by an electrostatic force of attraction to an electrostatic latent image formed on a photoreceptor drum. This allows a toner image based on electrostatic latent image to be formed on the photoreceptor drum.
Furthermore, recently, image forming apparatuses have been required to be higher in speed and smaller in size. This raises the need to charge a two-component developer quickly and sufficiently and also convey it quickly.
In order to disperse supplied toner into a two-component developer immediately and impart an appropriate amount of charge to the toner, an image forming apparatus employs a circulating developing device. The circulating developing device includes: a two-component developer conveying path serving as a route on which the two-component developer is circularly conveyed; and a two-component developer conveying member that conveys the two-component developer while agitating it in the two-component developer conveying path.
For example, Patent Literature 1 describes a developing device which does not apply undue force on a developer, which can disperse supplied toner into the developer immediately and impart an appropriate amount of charge to the toner, and which is highly capable of equalize the toner density of the developer in a developer storage section. That is, the developer storage section, in which a two-component developer obtained by mixing toner and carrier together is stored, is provided with a developer conveying path serving as a route on which the developer is circularly transported, and the developer conveying path has a developer conveying member provided therein, the developer conveying member having wing bars in the form of feed screws with a meshed screen member attached between the wing bars. The developer conveying member rotates to convey the developer. The developer is agitated by passing through the meshed screen member more than once. Friction between the toner and the carrier allows appropriate charging.